Ok Guys, why can't you just be "friends" with a pretty girl? 10 points best answer!?

Ok so i'm a 16 year old girl and although i don't think i'm pretty guys do, but anyway all these guys always get to know me and then want to get serious, want me to be there girlfriend, ect. I'm at a point in my life to where i don't need or want a bf to be happy, i'm independent and am just not interested at the moment. I'm focusing on school and getting into the best college and am also working on doing artwork and focusin on that talent. But anyway, i'm sort of shy but every guy that i think we can just be friends always drops the bombshell that they've fallen in love with me. Or so they say, There's this one guy, i've talked with for about a year or more but he's a few years older and doesn't live around here anymore. But we hung out the other day and he just dropped the bomb, "i think i like you as more of a friend." when they get mooshy gooshy and say something like that i don't feel as comfortable...We were pretty much best friends..now it just bothers me. Btw it could be because i have low self esteem and suffer from depression, but to me this just proves that guys can't just be friends with a pretty girl, i though this guy was diff. So guys, why is this so?